Welcome to the DEF ROM firmware generator. Upload your ROM, and we'll create a custom firmware with that ROM embedded.
Only Game Boy and Game Boy Color ROMs under 2MB are compatible.
This tool will automatically generate a valid firmware.bin file which you can then flash on your badge, check out my repo for instructions on how to flash .bin files.
Feel free to open an issue on the GitHub Repo or message @jaku and I'll try to help as best as I can.
If your stuff breaks, follow the UF2 flashing instructions here to restore your badge to the original firmware. I am not responsible for any broken badges, use this at your own risk.